A serial time-division multiplexing optical fiber sensing network with a large multiplexing capacity, which is based on identical ultraweak fiber Bragg gratings (FBGs) and self-heterodyne detection technique, is proposed. An experimental system, which has 10 identical ultraweak FBGs with the same Bragg wavelength of 1550 nm, reflectivity of −36 dB , and bandwidth of 0.1 nm, is set up to investigate the performance of the proposed scheme. The spectra of 10 ultraweak FBGs are resolved with a high accuracy, and the wavelength–temperature sensitivity and temperature resolution of the system are 10.5 pm/°C , 0.09°C, respectively. A self-heterodyne detection technique is adopted to increase the sensitivity of the receiver, which makes it possible to multiplex over 1000 FBGs along a single optical fiber. Theoretical analyses demonstrate that this sensing scheme can effectively increase the multiplexing capacity and measurement accuracy.